ui: change Queue to return all events at once

The Queue interface was changed from

	type Queue interface {
		Events(k Key) []Event
	}

to the more complex single-step protocol

	type Queue interface {
		Next(k Key) (Event, bool)
	}

to cater for a particular use case: Editor's SubmitEvent. When a
SubmitEvent is passed to a caller of Editor.Next, the Editor state,
in particular the current text, must not have changed by edits
later in the command stream. For example, pressing the keys <E>,
<Enter>, <E> should result in a SubmitEvent where the Editor has
a single 'e' in Text(), not two.

However, there is no reason to push the more complex Queue to every user.
Rather, store remaining input events inside Editor and process them as
Editor.Event (or Layout) is called.

Finally, revert the Queue interface to the simpler Events method.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/app/internal/input/router.go

@@ -37,8 +37,8 @@ type handlerEvents struct {
 	updated  bool
 }
 
-func (q *Router) Next(k ui.Key) (ui.Event, bool) {
-	return q.handlers.Next(k)
+func (q *Router) Events(k ui.Key) []ui.Event {
+	return q.handlers.Events(k)
 }
 
 func (q *Router) Frame(ops *ui.Ops) {
@@ -124,14 +124,12 @@ func (h *handlerEvents) Updated() bool {
 	return u
 }
 
-func (h *handlerEvents) Next(k ui.Key) (ui.Event, bool) {
-	events := h.handlers[k]
-	if len(events) == 0 {
-		return nil, false
+func (h *handlerEvents) Events(k ui.Key) []ui.Event {
+	if events, ok := h.handlers[k]; ok {
+		h.handlers[k] = h.handlers[k][:0]
+		return events
 	}
-	e := events[0]
-	h.handlers[k] = events[1:]
-	return e, true
+	return nil
 }
 
 func (h *handlerEvents) Clear() {

ui/app/window.go

@@ -323,8 +323,8 @@ func (w *Window) run(opts *windowOptions) {
 	}
 }
 
-func (q *Queue) Next(k ui.Key) (ui.Event, bool) {
-	return q.q.Next(k)
+func (q *Queue) Events(k ui.Key) []ui.Event {
+	return q.q.Events(k)
 }
 
 // WithTitle returns an option that sets the window title.

ui/doc.go

@@ -89,7 +89,7 @@ For example:
 
 	var queue ui.Queue = ...
 
-	for e, ok := queue.Next(h); ok; e, ok = queue.Next(h) {
+	for _, e := range queue.Events(h) {
 		switch e.(type) {
 			...
 		}

ui/gesture/gesture.go

@@ -105,8 +105,9 @@ func (c *Click) State() ClickState {
 }
 
 // Next returns the next click event, if any.
-func (c *Click) Next(q ui.Queue) (ClickEvent, bool) {
-	for evt, ok := q.Next(c); ok; evt, ok = q.Next(c) {
+func (c *Click) Events(q ui.Queue) []ClickEvent {
+	var events []ClickEvent
+	for _, evt := range q.Events(c) {
 		e, ok := evt.(pointer.Event)
 		if !ok {
 			continue
@@ -116,7 +117,7 @@ func (c *Click) Next(q ui.Queue) (ClickEvent, bool) {
 			wasPressed := c.state == StatePressed
 			c.state = StateNormal
 			if wasPressed {
-				return ClickEvent{Type: TypeClick, Position: e.Position, Source: e.Source}, true
+				events = append(events, ClickEvent{Type: TypeClick, Position: e.Position, Source: e.Source})
 			}
 		case pointer.Cancel:
 			c.state = StateNormal
@@ -125,7 +126,7 @@ func (c *Click) Next(q ui.Queue) (ClickEvent, bool) {
 				break
 			}
 			c.state = StatePressed
-			return ClickEvent{Type: TypePress, Position: e.Position, Source: e.Source}, true
+			events = append(events, ClickEvent{Type: TypePress, Position: e.Position, Source: e.Source})
 		case pointer.Move:
 			if c.state == StatePressed && !e.Hit {
 				c.state = StateNormal
@@ -134,7 +135,7 @@ func (c *Click) Next(q ui.Queue) (ClickEvent, bool) {
 			}
 		}
 	}
-	return ClickEvent{}, false
+	return events
 }
 
 // Add the handler to the operation list to receive scroll events.
@@ -159,7 +160,7 @@ func (s *Scroll) Scroll(cfg ui.Config, q ui.Queue, axis Axis) int {
 		return 0
 	}
 	total := 0
-	for evt, ok := q.Next(s); ok; evt, ok = q.Next(s) {
+	for _, evt := range q.Events(s) {
 		e, ok := evt.(pointer.Event)
 		if !ok {
 			continue

ui/input.go

@@ -5,9 +5,9 @@ package ui
 // Queue maps an event handler key to the events
 // available to the handler.
 type Queue interface {
-	// Next returns the next available event, or
-	// false if none are available.
-	Next(k Key) (Event, bool)
+	// Events returns the available events for a
+	// Key.
+	Events(k Key) []Event
 }
 
 // Key is the stable identifier for an event handler.

ui/text/editor.go

@@ -62,6 +62,9 @@ type Editor struct {
 	scrollOff image.Point
 
 	clicker gesture.Click
+
+	// events is the list of events not yet processed.
+	events []ui.Event
 }
 
 type EditorEvent interface {
@@ -71,7 +74,7 @@ type EditorEvent interface {
 // A ChangeEvent is generated for every user change to the text.
 type ChangeEvent struct{}
 
-// A SubmitEvent is generated when and Editor's Submit is set
+// A SubmitEvent is generated when Submit is set
 // and a carriage return key is pressed.
 type SubmitEvent struct{}
 
@@ -80,8 +83,8 @@ const (
 	maxBlinkDuration = 10 * time.Second
 )
 
-// Next returns the next available editor event, or false if none are available.
-func (e *Editor) Next(gtx *layout.Context) (EditorEvent, bool) {
+// Event returns the next available editor event, or false if none are available.
+func (e *Editor) Event(gtx *layout.Context) (EditorEvent, bool) {
 	// Crude configuration change detection.
 	if scale := gtx.Px(ui.Sp(100)); scale != e.oldScale {
 		e.invalidate()
@@ -106,7 +109,7 @@ func (e *Editor) Next(gtx *layout.Context) (EditorEvent, bool) {
 		e.scrollOff.Y += sdist
 		soff = e.scrollOff.Y
 	}
-	for evt, ok := e.clicker.Next(gtx.Queue); ok; evt, ok = e.clicker.Next(gtx.Queue) {
+	for _, evt := range e.clicker.Events(gtx.Queue) {
 		switch {
 		case evt.Type == gesture.TypePress && evt.Source == pointer.Mouse,
 			evt.Type == gesture.TypeClick && evt.Source == pointer.Touch:
@@ -124,7 +127,15 @@ func (e *Editor) Next(gtx *layout.Context) (EditorEvent, bool) {
 	if (sdist > 0 && soff >= smax) || (sdist < 0 && soff <= smin) {
 		e.scroller.Stop()
 	}
-	for ke, ok := gtx.Queue.Next(e); ok; ke, ok = gtx.Queue.Next(e) {
+	e.events = append(e.events, gtx.Queue.Events(e)...)
+	return e.editorEvent(gtx)
+}
+
+func (e *Editor) editorEvent(gtx *layout.Context) (EditorEvent, bool) {
+	for len(e.events) > 0 {
+		ke := e.events[0]
+		copy(e.events, e.events[1:])
+		e.events = e.events[:len(e.events)-1]
 		e.blinkStart = gtx.Now()
 		switch ke := ke.(type) {
 		case key.FocusEvent:
@@ -133,7 +144,7 @@ func (e *Editor) Next(gtx *layout.Context) (EditorEvent, bool) {
 			if !e.focused {
 				break
 			}
-			if e.Submit && (ke.Name == key.NameReturn || ke.Name == key.NameEnter) {
+			if e.Submit && ke.Name == key.NameReturn || ke.Name == key.NameEnter {
 				if !ke.Modifiers.Contain(key.ModShift) {
 					return SubmitEvent{}, true
 				}
@@ -166,7 +177,7 @@ func (e *Editor) Focus() {
 
 func (e *Editor) Layout(gtx *layout.Context) {
 	cs := gtx.Constraints
-	for _, ok := e.Next(gtx); ok; _, ok = e.Next(gtx) {
+	for _, ok := e.Event(gtx); ok; _, ok = e.Event(gtx) {
 	}
 	twoDp := gtx.Px(ui.Dp(2))
 	e.padLeft, e.padRight = twoDp, twoDp